This invention relates to a method and an apparatus for detaching fiber tufts from fiber bales, arranged in at least one series, by means of a fiber bale opener which travels along the fiber bales and whose detaching device may vary its height. The bale opener has a tower carrying the height-adjustable detaching device in a cantilever fashion and further, sensors are provided which detect the momentary height level of the fiber bales and also, feed reduction signals are calculated to ensure a progressive height equalization in case the bales of the series have different heights.
The surface of the fiber bales is seldom even, that is, it does not have a constant height. Such surface height within one bale series may vary significantly, dependent upon the origin of the fiber and the extent of compression, particularly when the pressure on the bales is relieved by removing the bale ties. The upper surface of the bales is, dependent upon the previously effective compression, different, even within a single fiber bale and particularly in case when several fiber bale rows are set up side-by-side. The upper bale surface has to be equalized. In case of long bale sets (for example, up to a length of 40 m), it is economically not feasible to horizontally align the bale set. In case a 40 m long bale set varies only about 0.5% (which is visually difficult to ascertain, if at all possible), a height difference of 350 mm is present.
According to a known process, the pressing rolls carried by the detaching device and bearing down on the bale surface are sensor rolls which may move vertically to a predetermined extent. The sensor rolls generate, by virtue of their radial excursion, an "up" signal via a sensor device which monitors the radial displacement of the sensor rolls and, applies the signal to the detaching device and, at the same time, also generates a feed reduction signal. According to such a process, the height of the respective fiber bale is determined in a purely mechanical manner without calculation and thus without computer support only during the respective passes over the fiber bale and a different detaching depth is set. It is a disadvantage of such a prior art method that after surface equalization of the bale series a constantly maintained feed for all the bales cannot be securely obtained. In the middle bale zones too, the feed is changed during radial motions of the sensor roll which may lead to undesired wavy motions of the detaching device in the middle zones. It is a further drawback that by virtue of the mechanical sensing by means of the sensor rolls the upper face of the bales is compressed which may affect the measuring magnitude.